1. Field of the Invention
The present invention relates to machine tools and more particularly to machine tools which are controlled in their operation in accordance with programs which are automatically executed to perform a variety of machining functions.
2. The Prior Art
Automatic controllers for machine tools are well known and are commonly referred to as numerical controls. Generally speaking such controls are relatively complicated and expensive, and machines which are equipped with sufficient controlling capacity to perform machining operation to close tolerances which are repeatable with very minor variations, are extremely expensive. Part of the reason for such complexity and expense is need to design special purpose apparatus for use in performing the programs of the NC controllers. It is therefore desirable to provide a system and method by which a high degree of accuracy in the performance and repeatability of machining operations can be attained without great expense or complexity.
In one class of machines, known as two axis machines, two axes are controlled by numerical control apparatus, but some information remains to be entered by the operator. In two-axis turret machining centers, the X and Y movements of tool versus work are controlled by numerical control, but the third or Z axis, which controls the depth of movement of the turret, which corresponds to depth of drilling, etc., must be entered by the operator by hand. Typically, mechanical cams and switches are used, to sense the turret or head position and to shift the feed rate from rapid to feed, when the tool approaches the work. Such cam operated switches are cumbersome and bulky, and as a result only a limited number of cam switches can be provided, with a corresponding limitation on the flexibility of the system. It is therefore desirable to provide a system and method by which the mechanical cam switches can be eliminated, and a larger number of different operations can be accommodated.
Although there have been efforts made in the past to produce electronic systems for replacing the mechanical cam switches, they have not been able to attain the optimum degree of flexibility. Accordingly, it is desirable to provide a system and method for providing an electronic system for replacing the mechanical cam operated switches which is unlimited in its flexibility and usefulness.